Significant growth in both high-frequency wired and wireless markets has introduced new opportunities where compound semiconductors such as SiGe have unique advantages over bulk complementary metal oxide semiconductor (CMOS) technology. With the rapid advancement of epitaxial-layer pseudomorphic SiGe deposition processes, epitaxial-base SiGe heterojunction bipolar transistors have been integrated with mainstream CMOS development for wide market acceptance, providing the advantages of SiGe technology for analog and RF circuitry while maintaining the full utilization of the advanced CMOS technology base for digital logic circuitry.
It is well documented that excess interstitials created by implant damage cause the formation of dislocations in the collector and emitter regions of bipolar devices. When the dislocations extend between the collector and emitter regions, bipolar pipe shorts, i.e., collector-emitter shorts, may occur. In such a context, SiGe bipolar yield can be reduced by as much as 20 to 50% for dislocations originating in the collector region.
The incorporation of C, carbon, into SiGe heterojunction devices has been carried out in the prior art to prevent the out-diffusion of boron into the base region. For example, it is known that the transient enhanced diffusion of boron is strongly suppressed in carbon-rich silicon layers; See, for example, H. J. Osten, et al., “Carbon Doped SiGe Heterojunction Bipolar Transistors for High Frequency Applications”, IEEEBTCM 7.1, 109. Boron diffusion in silicon occurs via an interstitial mechanism and is proportional to the concentration of silicon self-interstitials. Diffusion of carbon out of the carbon-rich regions causes an undersaturation of silicon self-interstitials. As a result, the diffusion of boron in these regions will be suppressed. Despite being capable of suppressing the diffusion of boron, prior art methods that incorporate C into the SiGe heterojunction bipolar structure do not prevent bipolar pipe shorts from occurring. Thus, prior art methods do not improve the SiGe bipolar yield.
In view of the SiGe bipolar yield problem mentioned above, there is a continued need for providing a new and improved method for improving SiGe heterojunction bipolar yield due to dislocations originating in the pedestal and collector regions of the device.